This invention relates generally to apparatus and methods of using the apparatus for drilling lateral or multi-lateral wells from an existing well bore, for the purpose of producing more oil and gas from the subsurface formations and for entry and reentry into said multi-lateral wells after they have been completed and for orienting and placing packers and/or other completion equipment in relation to these laterals and multi laterals. Specifically this invention relates to novel and improved assemblies and methods for the down hole milling of down hole windows and key-ways in communication with the down hole window for use in drilling and reentry of multilateral wells installation and completion of lateral well bores emanating from a main casing or a tubular walled member which may be vertical, deviated or horizontal and their entry or reentry.
Since it's inception horizontal drilling has offered a more efficient and cost effective means to produce oil and gas. This is primarily due to the advantage that horizontal drilling affords of economically exposing more of the hydrocarbon bearing reservoir to the wellbore. The recent introduction of multilateral drilling in which multiple horizontal or near horizontal wells are installed from a single vertical wellbore has extended the advantages of horizontal drilling while reducing the cost per foot of subsurface reservoir exposed, as well as reducing the amount of surface facilities required to develop an oil field. This has led to increased hydrocarbon production from multilateral wells. Until recently individual laterals were not cased or tied back to the main production casing. This meant that it was difficult or impossible to reenter these laterals in the event that workovers or stimulation was required.
The technology now exists to drill, tie back and complete multiple laterals in vertical, deviated, directional or horizontal wells either at the time the well is drilled or at a later time in the life of the well. More than one lateral can now be drilled, i.e., "Kicked Off" at the same elevation of the main casing in a well, and there is no limit as to how many laterals can be installed from a single main casing. However this has made the need for accurate placement of the positioning and drilling tools a crucial part of the drilling operation to achieve the desired results. The industry has relied on the accurate placement of "whipstocks", which are used to deflect the drill bit from the main casing at the desired location in a well to have a lateral drilled therein. In some cases a liner may be installed in the lateral and tied back to the main casing. Alternatively the laterals may be left unlined. In either case the whipstock is generally removed from the position of the drilled lateral, thus taking away the means to position or located the point of entry into the lateral well drilled unless some other positioning device is provided. As laterals in wells can be installed at the time the well is drilled or may be added at a future time if it is determined that incremental reservoir exposure is needed and it is determined that additional reservoirs may be accessed from the same wellbore, thus the industry has placed increasing importance on being able to selectively re-enter these laterals for workover operations, which makes accuracy of location of the lateral in the well bore important.
The equipment currently available in the industry is limited in allowing access to these laterals. Multilateral systems that employ premilled windows generally have a remotely located slots that are engaged by spring loaded lugs located on the whipstock which insure correct orientation to the window opening. These slots may be either tubular or rectangular in nature, and are located below the window opening. However these slots are limited to new wells as they must be installed in the casing string prior to the time that the casing is run. Also to reenter an existing well the general approach has been to set a packer below each window. This packer is used to land, anchor and orient the whipstock for both the drilling as well as any future reentry of the lateral for workover operations in the future. However allowing this packer to remain in the well restricts the ability to access the wellbore below this point. Alternatively removing the packer eliminates the possibility of reentering the lateral at a later date.
More recent prior system have been introduced to allow some type of reentry or detection device to land and anchor at the bottom of the window to allow the reentry of the lateral for workover purposes. Some drawbacks of these systems is their inherent inaccuracies in placement and unreliability in securing the deflection apparatus involved due to the inexact nature of the window which are milled downhole. These systems have been difficult to use because of the jagged, rough edges and metal shavings produced by the down hole milling of the window and can prevent the proper setting and alignment of such reentry tools. Up to this time all reentry systems have relied almost solely on using the raw cut bottom portion of the milled window to land and orient reentry devices.
Thus while there has been an increase in usage of the more advanced systems for lateral or multi-lateral well drilling in new wells, their use in existing wells has lagged behind. Though the number of multi laterals being drilled in existing wells has also increased, there has also been an increase in the problems associated with their installation because they are being used in more and varied well conditions and at more extreme angles of deviation from the vertical well bore than ever before. While there have been developed, many techniques to solve some of these problems they have only resulted in creating other and different problems. One of the most basic is providing a simple and universal assembly or assemblies and method or methods which can be used for both drilling and completion and also entry and reentry at a later date of a previously drilled well, even if that well has been drilled many years before because the cost are too great to pull or mill away the casing and set new casing with premilled window for drilling the desired multilateral wells needed in these wells.
The prior art has many approaches to solve this problem but most of them have required the mounting of keys, key-ways, slots, and packers permanently on the inside of the well bore and casing. While these approaches have had some success they have limited use because they reduce the access to some producing zones because they often project inwardly to the well , or in the case of an old well use a packer, which restricts access below this point in the well casing. Any system which restricts the operating diameter of the well bore also restrict the ability to operate other tools in the well passed the area were a multilateral has already been drilled. Due to the large forces used in wells created by the pipe and tools being moved up and down, these internal projections are subject to being damaged or destroyed by tools working in the casing, which would render the projections useless for their intended purpose. This is especially true for reentry of a drilled multilateral at a later date for additional workover of the multilateral. Thus the expense of the first multilateral well drilled could be completely lost, as well as access to that oil bearing strata without undertaking great additional expense.
Clearly multi-lateral drilling assemblies which have come under use in deeper and more complex older wells are more likely to have problems associated with retrieving and manipulating them in the well bores and successfully completing a multilateral. This is because the record keeping associated with these wells may have been lost or even if it exists, may not be as accurate as the records which are kept today. It is also more likely that numerous reentries or production operations undertaken on these wells over the years may have led to damage of the casing in certain areas.
In older well at greater depths a yet further problem is finding the exact location of the window which has been milled downhole and to properly orient the completion and production equipment to put that multilateral well in service. For example in a well have a depth of 10,000 feet, the spring in the drill string running tools can have several feet of movement or "slack" between the surface and downhole window. Further these well bores may not be straight down but instead contain sections, or "Cork Screws" in them from the previous drilling operations. The prior art has used spring loaded keys, for locating and orienting operations related to the geological formations for these lateral well bores. However many of these keys were equipped with multiple sets of keys which must mate with mounted key-receivers which were located in the main casing as part of the multilateral drilling process. This mating process could be a relatively complex arrangement and require diligence and accuracy in finding the correct key system. Also it required a very detailed and complicated record keeping procedure for any future work which might be done in the well for the future. Also as the various key-receivers for each well could be different it required the maintenance of a large inventory of each key system and this problem is growing as the number of such systems is increasing around the world.
In many of the prior art spring loaded key systems, the keys while easy to engage once the key was directly over the key hole or key way, these key holes and ways are normally of relatively small square area and a significant amount of time could be required for manipulating the drill string and tools to find the exact position to allow the key to spring out and mate with the key holes and key ways so that further work could be do. In most cases the keys had to hit key holes and ways with target areas measured in 25 to 50 square inches.
As the prior art often dealt with existing wells, which often used small target areas and which by nature are somewhat messy and unclean, these target areas can be completely fill up with metal shavings from earlier milling operations or formation cuttings which were generated when the lateral was drilled. In this case the spring loaded key would not have a space into which it could engage, with the corresponding problems of not being able to set other tools without additional work and runs back into the hole to clear the key hole or key ways.
Yet another problem in the prior art is the reentry of the at least one multi-lateral well once it has been drilled and completed, without leaving the whip stock and other orientation devices in the well. Leaving any of this equipment in the well would block other formations from having multilateral wells drilled in them, which is often not acceptable. Unfortunately removing this equipment left few if any means of identifying the entrance to the at least one multi-lateral well bore.
A further problem was even finding the down hole milled window because if the well is an older one many of the keys or indicators which were originally attached or fixed in the casing or tubular walls have been damaged or destroyed by other work that has occurred in the well since the drilling of the at least one multi-lateral well.
Also in the prior art the ability to reenter a well is many times totally dependant on the accuracy of the historical records kept on a well and the older the well the less likely the well records were likely to be available for use in the reentry process which rendered reentry either impossible or very expensive.
Further in the prior art the accuracy of reentry was not very good and while reentry was made it was not very accurately done with the corresponding wear and tear on the windows and key systems used, with a corresponding shortening of the life of the downhole milled window and it's keying system of what ever kind.